1. Field of the Invention
This invention relates to solid electrolyte fuel cell generation systems, and more particularly provides a method for processing reactants for such systems.
2. Description of the Prior Art
High temperature solid electrolyte fuel cells convert, through a usually exothermic electrochemical reaction, chemical energy into direct current electrical energy, typically at temperatures above 700.degree. C. The reaction takes place at the electrode-electrolyte interfaces where the electrolyte is sandwiched between an anode and a cathode. The reaction involves a relatively pure fuel, for example a mixture of hydrogen and carbon monoxide, and an oxidant such as oxygen or air. Where hydrogen and carbon monoxide fuel is utilized in a fuel cell based system, it is typically provided from a reformer, upstream of a fuel cell stack. The reformer reacts, for example, hydrocarbons, natural gas, or alcohols with steam in an endothermic process to produce a fuel suitable for the fuel cells, such as hydrogen and carbon monoxide mixtures.
The exothermic reaction in the fuel cells and heat released by other cell losses requires that a substantial cooling means be utilized. For example, relatively large amounts of cooling air are passed adjacent selected cell components. This may detract from overall system efficiency. Similarly, the endothermic reaction at the reformer requires substantial heat input, which also may detract from overall efficiency.
Many reformers operate with catalysts that are in limited supply, such as platinum. It is known that reformation can take place in that presence of less exotic materials, such as nickel. Also known is the use of cobalt for this purpose. Reformers upstream of the fuel cells have utilized particulated, or high surface area catalysts. Certain fuel cell configurations have been considered for so called indirect fuel cell systems. For example, FIG. 2.2 of a text entitled Fuel Cells For Public Utility And Industrial Power, Noyes Data Corp., 1977, and the accompanying description, refer to a molten carbonate electrolyte cell as a promising candidate for utilizing a hydrocarbon fuel reformed to hydrogen and CO at a nickel anode. The description also refers to an indirect solid-electrolyte fuel cell system wherein excess heat from the fuel cell system reaction at the cell is utilized as input to a coal gasification process. U.S. Pat. No. 3,462,306 also describes a liquid electrolyte fuel cell system having a nickel electrode which converts a mixture of methane (CH.sub.4) and water vapor into carbon dioxide and hydrogen.
Technical problems have, however, prevented such contemplated designs from achieving a system which is workable in practice. Concerns are typically raised relating to materials compatability and stability, reactant and product transport to and from the fuel cells, and particularly overall system efficiency.
It is thus desirable to provide a method of operating a fuel cell based system which offers increased system efficiency and alleviates other deficiencies of existing designs.